1. Field of the Invention
The present invention relates generally to analog-to-digital converters.
2. Description of the Related Art
To meet the requirements of modern signal processing systems, there is a continuing effort to increase the accuracy of the transfer functions of analog-to-digital converters. This accuracy is often measured by considering a converter error function that corresponds to the transfer function. A converter error function in the form of an integral nonlinearity function 17 is shown in the graph 16 of FIG. 1A. It is noted that the function ranges over a total excursion of approximately 2 least significant bits (LSBs).
It is further noted that there is a repeating pattern in the converter error function. In an exemplary subranging analog-to-digital converter, each repeating pattern may correspond to a subranging point of the first converter stage of the converter. One conventional linearization process thus provides converter calibration at these key subranging points to achieve the converter error function 19 shown in the graph 18 of FIG. 1B. However, calibration processes are generally limited in their improvement of the converter error function. For example, it is noted that the calibrated converter error function 19 still ranges over a total excursion on the order of 1.4 LSBs.